1. Field of the Invention
This invention relates to automatic door closing devices.
2. Description of the Prior Art
The present inventor has suggested a Japanese Pat. No. 30920/52 published on Aug. 11, 1977 on an automatic door closing device wherein, as shown in FIG. 1, an L-lever 3 is pivoted at one end on the short piece side with both right and left pieces as bearings 2 in the upper part of a channel-shaped fitting frame 1, a piston shaft 5 of a dash pot 4 is pivoted to the bending point 6 of the above mentioned L-lever 3, a cylinder 7 is pivoted also with both pieces of the lower part of the fitting frame 1 as a bearing 8 and a piston is pressed to one side by a spring contained in the dash pot 4 so that, when a door 9 is to be opened, by a hook plate 11 fitted to a wall frame 10, the L-lever 3 may be rotated against the above mentioned spring and may be locked when a dead point is passed and, on the other hand, when the door 9 is to be closed, just before it is closed, by the hook plate 11, the L-lever may be reversely rotated and, in case it is returned by the spring past the dead point, the dash pot 4 may be operated.
However, in this device, the prevention of oil leakage out of the dash pot 4 is made but is not perfect. During the long use, oil will leak out of the connecting part with a lid 12 screwed with the cylinder 7 or particularly the inserting part of the piston shaft 5 with the lid 12. As a result, there have been defects that the interior of the room will be stained and air will enter the cylinder 7 to fail it.
Further, in fitting such automatic door closing device to the door 9, it is screwed to the door 9 with the middle piece of the channel-shaped fitting frame 1. However, as the dash pot 4 fitted to the fitting frame 1 is in the way, it has been necessary to once remove the dash pot 4 from the fitting frame 1 and then to screw it. In fitting it, it has been necessary to fit the upper end of the fitting frame 1 to the upper end of the door 9 and to vertically position the device. Therefore, it has been very difficult to fit the device.
Further, in the conventional automatic door closing device, in the case of closing the door, a piston 13 will slide downward, a ball 14 will close a through hole 15, the passage of the oil in the cylinder 7 will be closed but, as the L-lever is gradually rotated, the oil will be leaked little by little from around the ball 14 in the structure. However, this structure requires a precision so high that it is not adapted to mass-production.